Technical Field
The present disclosure relates to a toner, a developer using the toner and a method of manufacturing toner.
Description of the Related Art
In electrophotography, electrostatic recording, electrostatic printing, etc., a toner is once adhered to a latent image bearer, such as an electrostatic latent image bearer, on which an electrostatic latent image has been formed in a process called developing process. The toner is then transferred from the electrostatic latent image bearer onto a transfer medium such as paper in a process called transfer process. The toner is then fixed on the transfer medium in a process called fixing process.
Recently, a polymerization toner produced by a suspension polymerization method and another toner produced by a polymer dissolution suspension method that causes volume contraction have been proposed. In order to give a toner chargeability and flowability in a developing unit and improve transfer property and prevent the toner from blocking each other, it is disclosed to combine an external additive with the polymerization toner. For example, the external additive is inorganic fine particles or organic fine particle.
A certain amount of toner particles remains on the latent image bearer without being transferred. Such residual toner particles should be removed from the latent image bearer so as not to prevent formation of a next electrostatic latent image. As a means for removing the residual toner particles, a blade cleaner is widely used, which has a simple configuration and high cleaning ability. It is known that as the shape of toner gets close to a sphere, it becomes more difficult to remove such toner and clean the latent image bearer. It is known that a layered compounds or inorganic filler is localized in the vicinity of the outer side of the toner so that the toner can be formed into an irregular shape in the suspension polymerization method.
In the above method of producing an irregular-shaped toner, a fine irregular structure on a surface of mother toner particles (particles not covered with any external additive) increases and BET specific surface area of the toner increases. And the external additive moves into concave portions of a surface of the mother toner particles. So an effective coverage of an external additive reduces. Consequently, in order to effect functions of flowability, chargeability and blocking resistance, it is necessary to combine the mother toner particles with a large amount of the external additive.
When a large amount of the external additive is added to the mother toner particles, flowability, chargeability and blocking resistance tend to increase, but retardation of fixation or following trouble are likely to occur.
(1) It changes substantially a developer charge amount that the free external additive adhere to a charging member such as carrier.
(2) It makes larger surface energy of a latent image bearer that the free external additive adheres to the latent image bearer.
Consequently, an output image is affected by toner filming.
(3) It makes larger surface energy of a developer holding member that the free external additive adhere to the developer holding member.
Consequently, an output image is affected by toner filming.
The toner made by a injection granulation method have been proposed instead of the polymerization toner. In the Injection granulation methods, raw materials of toner are dissolved or dispersed in an organic solvent, the resulting liquid (hereinafter “toner constituents liquid”) is discharged from uniform and fine discharge holes. And the discharged liquid droplets are dried into toner particles in a gas flow. This method can produce toner particles having a very narrow particle size distribution, because the toner constituents liquid is discharged from fine discharge holes. Also, this method can produce toner particles having a very narrow shape distribution, because a dissolving component or a dispersing component is included uniformly in the liquid droplet.
In the Injection granulation methods, a binder resin is used as the dissolving component, so a particle is soft as a whole. Consequently, the external additive will become easy to be embedded in mother toner particles. Furthermore, the liquid droplets are dried into toner particles in a gas flow in an instant, so the mother toner particles will become easy to have a truly spherical shape. When using toners having a truly spherical shape or a close truly spherical shape, there arises a problem in cleaning ability of the toners at the developing process. Against this, It is proposed that a shape of the toner is controlled by including a crystalline compound as the dissolving component or the dispersing component in the toner constituents liquid.
However, a surface of the mother toner has a fine irregular structure or wrinkles by forming into the irregular shape toner by the crystalline compound. So, BET specific surface area of the toner increases. When BET specific surface area of the toner increases, the effective coverage of an external additive reduces. So, it is necessary to combine the mother toner particles with a large amount of the external additive. When a large amount of the external additive is added to the mother toner particles, the above-mentioned troubles are likely to occur. Furthermore, the toner is likely to crush from the interface of the crystalline compound on the surface of the toner.
There are various ways of reducing BET specific surface area of the toner. For example, it is proposed to treat the toner with heat or solvent. However, when the toner is treated with heat or solvent, the toner likely adhere to each other. So, the toner particles have a wide particle size distribution. Also, there is concern that the release agent in the toner bleed to the surface of the toner.
In order to improve transfer efficiency, it is proposed to control the adhesive force by adjusting the circularity or BET specific surface area of the toner into a specified value. However, this relate to the polymerization toner. Further improvements are required in the particle size distribution or the shape distribution.
From the above, toner particles having a narrow particle size distribution, an irregular shape and small BET specific surface area are required.